[css] Box-Shadow on the left side of the element only

box-shadow: -15px 0px 17px -7px rgba(0,0,0,0.75);

The first px value is the "Horizontal Length" set to -15px to position the shadow towards the left, the next px value is set to 0 so the shadow top and bottom is centred to minimise the top and bottom shadow.

The third value(17px) is known as the blur radius. The higher the number, the more blurred the shadow will be. And then last px value -7px is The spread radius, a positive value increases the size of the shadow, a negative value decreases the size of the shadow, at -7px it keeps the shadow from appearing above and below the item.

reference: CSS Box Shadow Property