css3 如何实现圆边框的渐变? 如图

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		<span class="nt">div</span><span class="nd">:before</span> <span class="p">{</span><span class="k">content</span><span class="o">:</span><span class="s2">""</span><span class="p">;</span> <span class="k">display</span><span class="o">:</span><span class="k">block</span><span class="p">;</span> <span class="k">width</span><span class="o">:</span><span class="m">100px</span><span class="p">;</span><span class="k">height</span><span class="o">:</span><span class="m">50px</span><span class="p">;</span> <span class="k">margin-top</span><span class="o">:</span><span class="m">10px</span><span class="p">;</span> <span class="k">padding</span><span class="o">:</span><span class="m">10px</span><span class="p">;</span> <span class="k">padding-bottom</span><span class="o">:</span><span class="m">0</span><span class="p">;</span> <span class="n">box</span><span class="o">-</span><span class="n">sizing</span><span class="o">:</span><span class="k">border</span><span class="o">-</span><span class="n">box</span><span class="p">;</span>
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				<span class="k">right</span> <span class="k">top</span><span class="o">,</span>
				<span class="k">color</span><span class="o">-</span><span class="n">stop</span><span class="p">(</span><span class="m">0</span><span class="o">,</span><span class="m">#fff</span><span class="p">)</span><span class="o">,</span>
				<span class="k">color</span><span class="o">-</span><span class="n">stop</span><span class="p">(</span><span class="m">1</span><span class="o">,</span><span class="m">#fff</span><span class="p">)</span>
			<span class="p">)</span><span class="o">,-</span><span class="n">webkit</span><span class="o">-</span><span class="n">gradient</span><span class="p">(</span>
				<span class="n">linear</span><span class="o">,</span>
				<span class="k">left</span> <span class="k">top</span><span class="o">,</span>
				<span class="k">right</span> <span class="k">top</span><span class="o">,</span>
				<span class="k">color</span><span class="o">-</span><span class="n">stop</span><span class="p">(</span><span class="m">0</span><span class="o">,</span><span class="m">#077df8</span><span class="p">)</span><span class="o">,</span>
				<span class="k">color</span><span class="o">-</span><span class="n">stop</span><span class="p">(</span><span class="m">1</span><span class="o">,</span><span class="m">#74baff</span><span class="p">)</span>
			<span class="p">);</span>
			<span class="k">background</span><span class="o">-</span><span class="k">clip</span><span class="o">:</span><span class="k">content</span><span class="o">-</span><span class="n">box</span><span class="o">,</span><span class="k">padding</span><span class="o">-</span><span class="n">box</span><span class="p">;</span>
		<span class="p">}</span>
		<span class="nt">div</span><span class="nd">:after</span> <span class="p">{</span><span class="k">content</span><span class="o">:</span><span class="s2">""</span><span class="p">;</span> <span class="k">display</span><span class="o">:</span><span class="k">block</span><span class="p">;</span> <span class="k">width</span><span class="o">:</span><span class="m">100px</span><span class="p">;</span><span class="k">height</span><span class="o">:</span><span class="m">50px</span><span class="p">;</span> <span class="k">padding</span><span class="o">:</span><span class="m">10px</span><span class="p">;</span> <span class="k">padding-top</span><span class="o">:</span><span class="m">0</span><span class="p">;</span> <span class="n">box</span><span class="o">-</span><span class="n">sizing</span><span class="o">:</span><span class="k">border</span><span class="o">-</span><span class="n">box</span><span class="p">;</span>
			<span class="k">border-bottom</span><span class="o">-</span><span class="k">left</span><span class="o">-</span><span class="n">radius</span><span class="o">:</span><span class="m">50px</span><span class="p">;</span>
			<span class="k">border-bottom</span><span class="o">-</span><span class="k">right</span><span class="o">-</span><span class="n">radius</span><span class="o">:</span><span class="m">50px</span><span class="p">;</span>
			<span class="k">background</span><span class="o">:-</span><span class="n">webkit</span><span class="o">-</span><span class="n">gradient</span><span class="p">(</span>
				<span class="n">linear</span><span class="o">,</span>
				<span class="k">left</span> <span class="k">top</span><span class="o">,</span>
				<span class="k">right</span> <span class="k">top</span><span class="o">,</span>
				<span class="k">color</span><span class="o">-</span><span class="n">stop</span><span class="p">(</span><span class="m">0</span><span class="o">,</span><span class="m">#fff</span><span class="p">)</span><span class="o">,</span>
				<span class="k">color</span><span class="o">-</span><span class="n">stop</span><span class="p">(</span><span class="m">1</span><span class="o">,</span><span class="m">#fff</span><span class="p">)</span>
			<span class="p">)</span><span class="o">,-</span><span class="n">webkit</span><span class="o">-</span><span class="n">gradient</span><span class="p">(</span>
				<span class="n">linear</span><span class="o">,</span>
				<span class="k">left</span> <span class="k">top</span><span class="o">,</span>
				<span class="k">right</span> <span class="k">top</span><span class="o">,</span>
				<span class="k">color</span><span class="o">-</span><span class="n">stop</span><span class="p">(</span><span class="m">0</span><span class="o">,</span><span class="m">#fff</span><span class="p">)</span><span class="o">,</span>
				<span class="k">color</span><span class="o">-</span><span class="n">stop</span><span class="p">(</span><span class="m">1</span><span class="o">,</span><span class="m">#74baff</span><span class="p">)</span>
			<span class="p">);</span>
			<span class="k">background</span><span class="o">-</span><span class="k">clip</span><span class="o">:</span><span class="k">content</span><span class="o">-</span><span class="n">box</span><span class="o">,</span><span class="k">padding</span><span class="o">-</span><span class="n">box</span><span class="p">;</span>
		<span class="p">}</span>
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