Start by creating a 150×150 px document, with white background. Press Shift + F5 to fill the new layer with 353D44. Create a New Layer, select the Rounded Rectangle Tool and make a rounded rectangle (radious 10px) like this size:

Right-click the shape layer and Raterize Layer, now right-click it again and go to Blending Options:

Parts just needed to be edited will appear

Outer Glow
Blend Mode: Normal
Opacity: 60%
Color: Black (#000000)

Color Overlay
Color: 374756
Blend Mode: Normal
Opacity: 100%

If you want, you add a some white brush to the button:

Done that, create a New Layer (Control + Shift + N), insert your image or text (color: white) and resize the image or text you will use. Right-click layer and go to Blending Options:

Parts just needed to be edited will appear

Outer Glow
Blend Mode: Overlay
Color: White
Size: 10px

If you wont add anything else, then create a New Layer. Holding Control, click on the button layer (rectangular rounded shape) and with the Rectangular Marquee Tool make a selection (holding Alt) of the bottom-half part of the rounded rectangle:

Now, fill that selection with White and apply the White to Transparent 4 style:

*If you dont have this style, click the blue arrow in the Styles Windows and select Web Styles and click Append, now just go to the bottom of the styles list.

Next, just change the Gradient Overlay blend mode to Soft Light:

And thats it! For your site, just use the different colors needed.